1. Field of Invention
Ramp devices for loading wheeled vehicles into the bed of a truck or trailer. In particular, locking devices on such ramps to prevent accidental release of the ramp from the vehicle.
2. Description of Prior Art
In the past, the tailgates of pickup type trucks lowered to a vertically hanging position and ramps could be hooked onto the hinged edge of the tailgate or directly to the truck bed. Recent designs of pickup trucks permit the tailgate to be lowered only to approximately horizontal or slightly lower position. There is no provision or design feature that permits attaching accessories such as a set of ramps to the tailgate. Furthermore, there is a significant gap between the tailgate and the truck bed over which a load has to be slid or carried.
Loading ramps for pickup trucks may be classified in several functional groupings:
A. Ramp systems where the tailgate or equivalent takes no part in the loading of the truck. These are where either the tailgate is removed, dropped below the ramp, or the ramps pass over the tailgate without co-operative interaction. These are different in form, function, and way used from the present invention. U.S. Pat. Nos. 5,553,762 and 5,810,546 and D 360,729 and D 398,129 and D 354,603 are typical of this type of ramp system. Many modern trucks are designed so that the tailgate cannot be lowered below horizontal position, precluding dropping it out of the way. Ramp systems that pass over the tailgate in closed position place the load high on the truck which can cause unstable operation of the truck while driving.
B. Ramps systems that connect to the free edge of the tailgate, bumper, or some part of the truck, but where the load is rolled directly on the tailgate surface. This subjects this surface of the tailgate to denting and paint marring. These, also, require rolling the load over the gap between the tailgate and the bed. Attaching to the free end of the tailgate requires either modification of the tailgate or installation of a harness device to which the ramps attach directly. U.S. Pat. Nos. 4,795,304 and 4,098,414 and 3,976,209 and D 316,771 are typical of tailgate edge mounted loading ramps. These all require modification to the truck to install the ramp systems.
The present invention requires no removing of parts, and no drilling, cutting, or any permanent fastening to the truck. The present invention does not require modification to the truck to attach the ramp, and the load is rolled over a portion of the ramp system positioned to protect most of the tailgate from any damage.
C. Ramp systems which convert between a ramp function and a tailgate function. This type of system usually uses either telescoping or unfolding to extend the ramp for use. U.S. Pat. Nos. 5,907,267 and 5,273,335 are typical examples. Ramps of this type require removal and replacement of the original equipment tailgate. The present invention does not require removal of the original tailgate.
Ramps that fold or telescope in the middle to shorten them for storage inherently have a weak spot at the joint. A hinge, telescoping, or bolted joint in the sloping portion of a ramp is required to resist considerable bending moments because he bending moment of a ramp with simple end supports is maximum at the center. This type of design requires either the loads be severely limited, external supports be provided, or that the ramps be heavy structures. The present invention has a hinged clamp at one end of the sloping ramp portion. Here the bending strength requirement is less than in the middle of a simply supported ramp.
Some ramps may be classified in more than one of the above groupings, however, that does not negate the analysis of their form, function, and way of use.
None of the references cited acknowledge that there is a gap between the original equipment tailgate and the truck bed, and of course, none teach any means to overcome having to roll the load over such a gap. U.S. Pat. No. D 360,729, by Gary B. Collins, and U.S. Pat. No. 5,810,546, by Ralph Schmoling, ignore the problem, but also appear to avoid the problem by installing a secondary bed or rack designed specifically for the intended load. Collin's has a track/frame assembly for carrying an ATV (All Terrain Vehicle) and includes specific tie-down rings. Schmoling's has a general frame and a contoured set of frames carrying rollers for loading and supporting a boat. Neither use any part of the truck directly for supporting the load, thus they passed over the gap without having to consider it. U.S. Pat. No. 5,273,335, by Philip Belknap, has what at first appears to be a cover over the gap. Upon closer examination, plate (44) is not a gap cover, but a ramp leading down from the ramp/tailgate structure. This is required in the Belknap design because the original tailgate was replaced by the combination ramp/tailgate attached inside, and above, the truck bed. Belknap's design also makes an extra and objectionable drop into the truck. Conversely, a lift is required to move the load from the bed to the Belknap ramp.